Ultrasound imaging apparatus and methods

ABSTRACT

Ultrasound imaging apparatus and method for veterinary applications. An ultrasound probe obtains ultrasound frame data which is compressed prior to wireless communication to a data processing unit. The data processing unit decompresses the ultrasound frame data and uses it to generate ultrasound images. The transmit bandwidth or transmit buffer size are monitored and the scan rate is reduced if required to maintain low latency. The apparatus generates images with lower latency and greater tolerance of variations in wireless data transfer bandwidth than where images are generated by an ultrasound probe and transmitted wirelessly to a remote display. A regularly updated image can be displayed even if image quality may be temporarily reduced.

FIELD OF THE INVENTION

The invention relates to the field of ultrasound imaging apparatus andmethods for medical, particularly veterinary, ultrasound imaging. Theapparatus comprises an ultrasound scanner which makes ultrasound signalmeasurements and a separate ultrasound data processor which generatesreal-time images.

BACKGROUND TO THE INVENTION

It is known to provide ultrasound scanners for veterinary use whichgenerate streaming video data, in a format such as MPEG, and whichtransmit that video data wirelessly, for example though a W-iFiconnection, to a separate display device, such as a dedicated ultrasounddisplay device, smart phone, or tablet, to enable a user to view thescanned tissue in real time. They are typically handheld or at leasthave a handheld probe.

Veterinary ultrasound scanners are often used in challengingenvironments, for example outdoors, or in farm buildings. Environmentalfactors (such the presence of walls, metal objects etc.), combined withmovement of both the scanner and the display device mean that Wi-Fi datatransmission speed and reliability may well be substantially below whichcan be achieved in optimum conditions and may vary intermittently. Thiscan lead to poor quality image transmission, for example, video maysuffer a drop in quality, freeze, or be lost.

Another problem arising from limitations in Wi-Fi data transmissionspeed and reliability is that of a high latency, i.e. a high timedelay/lag between ultrasound data sampling and display of the resultingimage. Even a latency of 0.25 seconds, for example, substantiallyreduces the utility of a handheld ultrasound scanner.

Known handheld scanners with wireless data transmission interfacestypically generate images in an MPEG format. By an MPEG format we referto a format approved by the Moving Pictures Expert Group, including butnot limited to MPEG-1 (ISO/IEC 11172), MPEG-2 (ISO/IEC 13818), MPEG-4(ISO/IEC 14496), MPEG-7 (ISO/IEC 15938), MPEG-21 (ISO/IEC 21000). MPEGand similar formats compress images in a “group of pictures” or GOPstructure, which are effectively a collection of consecutive images in acoded video stream. Each group of pictures is encoded using intra frameand inter frame compression techniques and the compressed data structureincludes I frames (intra coded picture frames) which are effectivelyreference frames, coded independently of other pictures, as well asother frames (P frames and B frames) which include motion-compensatedinformation about differences between consecutively decompressedpictures. The inventors have found that when using MPEG and other imagecompression formats with a GOP structure is that there is inherently asignificant latency arising from the need to store each of the group ofpictures before they can be encoded and transmitted. The number ofpictures which are included in a single group is known in the art as theGOP size, or GOP length and is typically at least 6, and often more inorder to facilitate better compression (e.g. 12, 15 or 18). The latencyintroduced by encoding in MPEG or another format using a group ofpictures structure can present a significant reduction in ease of use inreal-time ultrasound scanning, particularly in veterinary applicationswhere the hand and probe cannot be visualised and the operator must relysolely on ultrasound imaging for probe positioning. This cannot bereadily overcome by increasing sampling rate as that would both increasepower consumption and fail where bandwidth was limited.

The invention seeks to address one or more of the problems set outabove.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided (e.g.veterinary) ultrasound imaging apparatus comprising an ultrasoundscanner and a separate ultrasound data processor:

the ultrasound scanner comprising:

-   -   one or more ultrasound sources and receivers,    -   transmit circuitry configured to apply electrical signals to the        ultrasound sources to transmit ultrasound pulses into a scan        region,    -   receive circuitry configured to measure ultrasound echoes        received at the ultrasound receivers from the scan region,    -   a beam processor configured to process the measured ultrasound        echoes and output ultrasound frame data, the ultrasound frame        data comprising measurements of ultrasound echoes from each of a        series of scan positions in the scan region,    -   a data compressor configured (e.g. programmed) to process        ultrasound frame data output by the beam processor to generate        compressed ultrasound frame data, and    -   a wireless transmitter configured to wirelessly transmit the        compressed ultrasound frame data;

the ultrasound data processor comprising:

-   -   a wireless receiver configured to receive the compressed        ultrasound frame data transmitted by the wireless transmitter,    -   a data decompressor configured to decompress compressed        ultrasound frame data received by the wireless transmitter,    -   an image processor configured to process decompressed data        output by the data decompressor to form ultrasound images of the        scan region, and    -   a display interface (and typically also a display, although the        display interface may be a video data output interface, for use        with a separate display) configured to output the ultrasound        images formed by the image processor.

The invention extends in a second aspect to a method of processingultrasound echo data to form images (e.g. of a region of a non-humananimal), the method comprising:

at an ultrasound scanner comprising one or more ultrasound sources andreceivers, receiving ultrasound echoes from a scan region,

processing measurements of the received ultrasound echoes to therebycalculate ultrasound frame data, the ultrasound frame data comprisingmeasurements of ultrasound echoes from each of a series of scanpositions in the scan region,

compressing the ultrasound frame data to generate compressed ultrasoundframe data,

transmitting the compressed ultrasound frame data through a wirelesstransmitter to a wireless receiver of an ultrasound data processor,

at the ultrasound data processor, decompressing the received ultrasoundframe data, processing the decompressed data to form ultrasound imagesof the portion of the subject, and outputting the ultrasound images (forexample displaying the ultrasound image or outputting video data throughan interface).

The method typically also comprises controlling transmit circuitry toapply electrical signals to the ultrasound sources to transmitultrasound pulses into the scan region (thereby leading to saidultrasound echoes from the scan region).

Accordingly, the ultrasound frame data is compressed prior to beingtransmitted through a wireless communications channel comprising thewireless transmitter and the wireless receiver. The compressedultrasound frame data is then decompressed and used to generate images.This enables reduced latency in comparison to known ultrasound scannerswhich generate video images using MPEG or another group of picturescompression technique. The ultrasound images are typically presented asvideo images.

The wireless transmitter and receiver are typically radio transmittersand receivers. Typically, they are radio transceivers. It may be thatthe wireless transmitter and receiver are Wi-Fi transmitters andreceivers (e.g. Wi-Fi transceivers). Thus, the compressed data may betransmitted by Wi-Fi. Wi-Fi is a wireless radio transmission protocolspecified by the IEEE 802.11 standards. (Wi-Fi is a trade mark of theWi-Fi Alliance).

The invention is particularly relevant when the compressed data istransmitted by Wi-Fi. Wi-Fi is convenient to use as it is found in manycommon computing devices but Wi-Fi can have varying and unreliablebandwidth when implemented outdoors or in other field sites typical inveterinary applications. The invention improves image quality and/orreduces latency.

The measurements of ultrasound echoes from each of a series of scanpositions in the scan region typically comprise data (samples)specifying the measured strength of ultrasound echoes received by one ormore ultrasound receivers from the corresponding position within thescan region. By the strength of ultrasound echoes we refer to aparameter relating to the intensity, amplitude or brightness of theultrasound echoes, in absolute terms or relative to the incidentultrasound pulses.

The transmit circuitry is typically also configured to focus transmittedultrasound pulses on each of the plurality of scan positions in the scanregion in turn. Typically, transmitted ultrasound pulses radiate along anarrow beam and thereby reach a plurality of scan positions along a scanline in turn. The person skilled in the art is familiar with beamprocessors capable of focussing transmitted ultrasound pulses onspecific position in a scan region and beam processors capable ofprocessing the output of ultrasound receivers to determine the measuredstrength of echoes received from specific scan positions.

Typically, the ultrasound scanner comprises an ultrasound probe region(for example an ultrasound probe), the ultrasound probe regioncomprising the one or more ultrasound sources and receivers. The one ormore ultrasound sources and receivers may be an array of ultrasoundsources and receivers. The array of ultrasound sources and receivers istypically in the form of a one dimensional array, for example spacedapart along a linear or curved line. However, it is possible that theone or more ultrasound sources and receivers is mounted on a support andis swept repetitively along a path in use. In this case a singleultrasound source and a single ultrasound receiver (e.g. a singleultrasound transceiver) may be sufficient.

The scan region is typically planar (being a cross-section through aregion of a subject, in use). The scan region is typically defined bythe configuration of the ultrasound sources and receivers, and thetransmit circuitry and beam processor.

The transmit circuitry is typically configured to focus transmittedultrasound pulses on a plurality of scan positions in the scan region inturn (typically a plurality of scan lines which are scanned in turn,each having a plurality of spaced apart scan positions which are scannedin turn as ultrasound pulses focussed on the scan line pass into thetissue). The person skilled in the art is familiar with beam processorscapable of focussing transmitted ultrasound pulses on specific lines ina scan region and beam processors capable of processing the output ofultrasound receivers to determine the measured strength of echoesreceived from specific scan positions.

The scan region is typically scanned as a series of scan lines,extending from the ultrasound probe region (i.e. from the array one ormore ultrasound transmitters and receivers, or the path along which oneor more ultrasound transmitters and receivers are repetitively swept,where appropriate) at different angles. The plurality of scan positionsin the scan region typically comprises a plurality of scan positionsspaced apart (usually regularly) along each of a plurality of scan lineswhich extend through the scan region at different angles relative to theultrasound probe region (i.e. from the array of ultrasound transmittersand receivers, or the path along which one or more ultrasoundtransmitters and receivers are repetitively swept, where appropriate).

The ultrasound frame data typically comprises ultrasound line dataportions which specify the measured strength (e.g. intensity oramplitude) of ultrasound echoes received by one or more ultrasoundreceivers from a series of spaced apart positions along a line(typically a straight line extending from the ultrasound probe regioninto the scan region). Typically, the ultrasound frame data comprises aplurality of ultrasound line data portions each of which relates to adifferent line extending into the scan region and which have beenmeasured consecutively. Typically each relates to a line extending at adifferent angle from the ultrasound probe region into the scan region.Typically, the lines extend at different angles in the same plane.Typically the lines are in a cross-section through a region of thesubject, in use.

Typically, the ultrasound frame data is divided into ultrasound frames,each of which represents measurements of ultrasound echoes across thescan region, suitable for forming an image frame. In this case, eachultrasound frame comprises a plurality of ultrasound line data portionsextending through the scan region, e.g. at different angles relative tothe ultrasound probe region (i.e. the array of ultrasound sources andreceivers, or the path along which one or more ultrasound transmittersand receivers are repetitively swept, as appropriate). It is not howevernecessary for each ultrasound frame portion to have ultrasound line dataportions relating to the same angles relative to the ultrasound probe,for example, ultrasound line data portions relating to different scanlines (angles relative to the ultrasound prove region/array ofultrasound sources and receivers, or the path along which one or moreultrasound transmitters and receivers are repetitively swept, whereappropriate) may be included in alternate ultrasound frame datastructures.

By an ultrasound image we refer to a visual representation, in at leasttwo dimensions, of the scan region as indicated by the ultrasound echoeswhich are received by the at least one ultrasound receiver, in responseto ultrasound signals being generated by the at least one ultrasoundtransmitter. The ultrasound images are typically frames of video images.The ultrasound images are typically pixelated, for example twodimensional pixelated images. The pixels typically represent parts ofthe image in a rectangular array. In the present invention, theultrasound images are obtained by processing ultrasound frame data whichhas been compressed, transmitted wirelessly, and decompressed.Typically, the processing of the decompressed image data to form anultrasound image comprises scan conversion. The processing of thedecompressed image data to form an ultrasound image may comprise one ormore of: angle compounding, frame smoothing and boundary detection. Theimage processor may comprise a scan converter. The image processor maycomprise one or more of: an angle compounder, a frame smoother and aboundary detection module.

The data compressor is preferably configured to compress each ultrasoundframe of ultrasound frame data separately. The data compressor ispreferably configured to output compressed ultrasound frame data inwhich each individual ultrasound frame is compressed independently ofany other frame. Data compression preferably comprises processingindividual ultrasound frames separately. Data compression preferablygenerates data portions each of which represents an individualultrasound frame without reference to any other frame. This contrastswith group of picture type data compression techniques which output datarepresenting differences between consecutive images/frames (along withreference frames).

The data compressor may be configured to compress each individualultrasound line data portion separately. The data compressor may outputcompressed ultrasound frame data in which each individual ultrasoundline is compressed separately. Data compression may comprise processingindividual line data portions separately. Data compression may generatedata portions each of which represents an individual ultrasound linedata portion without reference to any other ultrasound line data.

By compressing each ultrasound frame, and in some embodiments eachultrasound line, separately, latency can be reduced. Furthermore, insome embodiments introduced below in which in some circumstances thescan rate or bandwidth of transmitted data is selectively reduced, thiscan be done without delay as frames (or lines respectively) need noteach have the same size.

The ultrasound frame data may comprise ultrasound line data portionswhich specify the measured strength of ultrasound echoes received by oneor more ultrasound receivers from a series of spaced apart positionalong a line. The data compressor may be configured to output compressedultrasound frame data in which each individual ultrasound line iscompressed separately and/or wherein the data compressor is configuredto calculate and encode the differences between consecutive measurementswithin ultrasound line data portions

The data compressor may be a variable length code compressor. The datacompressor may be configured to calculate and encode the differencesbetween consecutive measurements within ultrasound line data portions.The step of compressing the ultrasound frame data may comprise applyinga variable length code compression algorithm to the ultrasound framedata. Typically, the method comprises calculating the difference betweenmeasurements (typically consecutive measurements) of the strength ofultrasound echoes within ultrasound data lines and encoding thesedifferences, for example using a variable length code. Using a variablelength code typically comprises selecting, from amongst a group ofcodes, which includes codes of a plurality of different bit lengths, acode representative of the respective difference. We have found thatvariable length codes are efficient for compressing ultrasound linedata.

The ultrasound scanner may be configured to regulate (e.g. reduce) thenumber of scan positions per unit of measurement time of the ultrasoundframe data which is transmitted by the wireless transmitter, incompressed form, typically responsive to a received variable relating toa transmission property of the wireless transmitter. The method maycomprise receiving a variable relating to a transmission property of thewireless transmitter and varying (e.g. reducing) the number of scanpositions per unit of measurement time of the ultrasound frame datawhich is transmitted by the wireless transmitter, in compressed form,responsive thereto.

We refer to the number of scan positions per unit of measurement time inrespect of which data is transmitted (in compressed form) because thisdetermines the rate at which data for transmission accumulates.

The transmission property of the wireless transmitter may be related tothe current transmission bandwidth of the wireless transmitter. Thetransmission property of the wireless transmitter may be related to thecurrent delay between data being queued for wireless transmission andthe data being transmitted, for example, a parameter related to theamount of data in a transmit buffer of the wireless transmitter (forexample a measurement of the amount of data in the transmit buffer, orthe spare capacity of a transmit buffer (of defined size), or theestimated time until the buffer has a certain amount of data storedtherein, e.g. is full).

It may be that the number of scan positions per unit of measurement timeof the ultrasound frame data is reduced responsive to detection that theamount of data in the transmit buffer exceeds a threshold.

It may be that the variable relating to the transmission capacity of thewireless transmitter is a time-varying parameter indicative of thecurrent transmission bandwidth of the wireless transmitter to thewireless receiver.

The number of scan positions per unit of measurement time in respect ofwhich compressed ultrasound frame data is transmitted may be regulated(e.g. reduced) by reducing the number of scan positions per unit ofmeasurement time in respect of which compressed ultrasound frame data istransmitted, for example, by one or more of:

-   -   regulating (e.g. reducing) the number of scan positions per scan        line in respect of which compressed ultrasound frame data is        transmitted;    -   regulating (e.g. reducing) the number of scan lines per        ultrasound frame in respect of which compressed ultrasound frame        data is transmitted;    -   regulating (e.g. increasing) the period (of measurement time)        between ultrasound frames in respect of which compressed        ultrasound frame data is transmitted.

This enables the number of scan positions per unit of measurement timein respect of which data which is transmitted to be varied rapidly inresponse to changing properties of the transmission of data wirelessly.Thus, if there is a decrease in available bandwidth, or an increase inthe amount of data queued in the buffer for transmission, the amount ofdata per unit of measurement time which is transmitted can be reduced,so that the available bandwidth is sufficient to transmit the resultingcompressed data and/or the size of the buffer is reduced.

It is better to reduce the number of scan positions in respect of whichultrasound frame data is transmitted, which may cause a degradation ofimage quality, than to lose continuity of image formation and output.Accordingly, preferably, in at least some circumstances reducing thenumber of scan positions in respect of which ultrasound frame data istransmitted leads to some degradation of image quality (e.g. resolutionand/or frame rate) but without a break in ultrasound image formation andoutput.

It may be that the number of scan positions per unit of time in respectof which compressed ultrasound frame data is transmitted is regulated(e.g. reduced) progressively through a plurality of different modes,which differ in terms of the number of scan positions in respect ofwhich compressed ultrasound frame data is transmitted, in apredetermined order, the modes differing in terms of one or more of: thenumber of scan positions per scan line, the number of scan lines perultrasound frame and/or the period between ultrasound frames. It may bethat the apparatus is configured to vary the number of scan positionsper unit of measurement time in respect of which data is transmittedwithin an ultrasound frame.

It may be that the number of scan positions per unit of measurement timein respect of which compressed ultrasound frame data is transmitted isvaried (e.g. reduced) progressively (responsive to measurements of thevariable relating to a transmission property of the wirelesstransmitter) through a plurality of different modes, which differ interms of the number of scan positions in respect of which compressedultrasound frame data is transmitted, in a predetermined order. Themodes may differ in terms of one or more of: the number of scanpositions per scan line, the number of scan lines per ultrasound frameand/or the period between ultrasound frames.

The number of scan positions per unit of measurement time in respect ofwhich data is transmitted may be varied within an ultrasound frame. Forexample, the number of scan positions per scan line in respect of whichcompressed ultrasound frame data is transmitted may change during anultrasound frame. The angular spacing between scan lines in respect ofwhich compressed ultrasound frame data is transmitted may change duringan ultrasound frame. Thus, it may be that not only can the number ofscan positions per scan line and/or the number of scan lines perultrasound frame/angular spacing between scan lines change from oneultrasound frame to the next but they may change within an ultrasoundframe. This enables a rapid response to changes in bandwidth and wouldnot be possible if the ultrasound frame data was converted into imagesand transmitted using MPEG, which requires the same number of pixels perpicture.

It may be that when the number of scan positions per unit of measurementtime in respect of which compressed ultrasound frame data is transmittedis regulated (e.g. reduced), the number of scan positions per unit ofmeasurement time in respect of which ultrasound echoes are generated isnot changed (e.g. reduced).

It may be that some ultrasound frame data, for example the ultrasoundline data relating to a subset of lines, or the measurements of echoesfrom a subset of the scan positions in respect of which measurements aretaken, is not transmitted in compressed form, for example, it may not becompressed and transmitted, or it may be compressed and not transmitted.For example, data concerning a subset of independently compressed scanlines may be discarded.

However, it may be that the ultrasound scanner is configured to regulate(e.g. reduce) the number of scan positions per unit of time which arescanned (i.e. in respect of which ultrasound pulses are focussed on),typically responsive to a received variable relating to a transmissionproperty of the wireless transmitter. This will thereby regulate (e.g.reduce) the number of scan positions per unit of measurement time of theultrasound frame data which is transmitted by the wireless transmitter,in compressed form. The method may comprise receiving a variablerelating to a transmission property of the wireless transmitter andvarying (e.g. reducing) the number of scan positions per unit of timeupon which ultrasound pulses are focussed responsive thereto (typicallyby reducing the number of scan lines which are scanned per unit oftime). This again regulates (e.g. reduce) the number of scan positionsper unit of measurement time of the ultrasound frame data which istransmitted by the wireless transmitter, in compressed form.

This has the advantage of not only reducing the amount of data which isgenerated for transmission, and thereby maintaining image quality and oravoiding excessive latency, it also has the advantage of reducing therate at which ultrasound pulses are generated and thereby reduces powerconsumption.

The number of scan positions per unit of time which are scanned may beregulated (e.g. reduced) by:

-   -   regulating (e.g. reducing) the number of scan positions per scan        line;    -   regulating (e.g. reducing) the number of scan lines per        ultrasound frame;    -   regulating (e.g. increasing) the period between ultrasound        frames.

It may be that the number of scan positions per unit of time which arescanned is varied (e.g. reduced) progressively (responsive tomeasurements of the variable relating to a transmission property of thewireless transmitter) through a plurality of different modes, whichdiffer in terms of the number of scan positions which are scanned, in apredetermined order. The modes may differ in terms of one or more of:the number of scan positions per scan line, the number of scan lines perultrasound frame and/or the period between ultrasound frames.

The ultrasound scanner typically comprises (or is in the form of) ahandheld ultrasound probe, i.e. an ultrasound probe configured to beused while held in a single hand by a user. Thus, the ultrasound scannermay comprise an ultrasound probe including the ultrasound probe region.In this case the ultrasound scanner typically also comprises anultrasound scanner body to which the ultrasound probe is connected inuse (e.g. through a cable). The ultrasound scanner may comprise anintegral body which is handheld and comprises the ultrasound proberegion. Typically, the ultrasound scanner comprises one or morebatteries. Typically the ultrasound scanner is powered only by the oneor more batteries in operation. Power consumption is an importantconsideration in ultrasound scanners powered only by one or morebatteries within the scanner.

The ultrasound scanner typically comprises a controller which regulatesthe rate at which scan positions are scanned. The ultrasound scannertypically comprises at least one processor and memory which stores aprogram which causes the at least one processor to function as thecontroller when executed. The transmit circuitry, the receive circuitry,the beam former and/or the data compressor may be formed in whole or inpart by the processor executing a program stored in the memory.Dedicated transmit circuitry, receiver circuitry and beam former ICs areknown in the art.

The ultrasound data processor typically comprises one or more processorsand memory storing program code. The ultrasound data processor may be ahandheld electronic device, for example a smartphone, tablet or laptop.The image display may be in wired communication with the imageprocessor. However, the image display may be in wireless communicationwith the image processor, for example the image display may comprisevideo glasses in wireless communication with the image processor. Thedata decompressor and/or image processor may be implemented in whole orin part by a microprocessor of the ultrasound data processor executingprogram code stored in a memory. The image processor may be implementedin whole or in part by a graphic processor.

One skilled in the art will appreciate that although the one or moreultrasound sources and receivers may comprise one or more ultrasoundsources and one or more separate ultrasound receivers, the one or moreultrasound sources and receivers may comprise one or more ultrasoundtransducers (e.g. an array of ultrasound transducers or one or moreultrasound transducers swept repetitively along a path during use), forexample piezoelectric transducers or capacitive transducers, whichfunction as both ultrasound sources and receivers.

Preferably, the time lag between ultrasound echoes being received by theultrasound receivers and the final (remote) display of the ultrasoundimage calculated by processing measurements of those ultrasound echoesis less than 0.2 seconds or less than 0.1 seconds.

Preferably, the time lag between ultrasound echoes being received by theultrasound receivers and the final (remote) display of the ultrasoundimage calculated by processing measurements of those ultrasound echoesis less than 6 times, and more preferably less than 3 times the periodbetween ultrasound frames.

The apparatus and method may be used to scan a region of an animal,typically a non-human animal, for example a farm animal (e.g. a pig,horse, cow or sheep) or a domestic animal (e.g. a cat or a dog).

DESCRIPTION OF THE DRAWINGS

An example embodiment of the present invention will now be illustratedwith reference to the following Figures in which:

FIG. 1 is a block diagram of ultrasound apparatus;

FIG. 2 is a schematic diagram of scan positions located along scan lineswithin a scan region;

FIG. 3 is a flow diagram of an ultrasound apparatus operating procedure;and

FIG. 4 is a block diagram of ultrasound frame data.

DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT

With reference to FIGS. 1 and 2, ultrasound scanning apparatus accordingto the invention comprises a handheld ultrasound scanner 2 and aseparate ultrasound data processor 4, which may be a dedicated computingdevice or a smart phone or tablet running a suitable applicationprogram, such as an iPhone, iPad or other iOS device (iPhone, iPad andiOS are trade marks of Apple Inc.) or a mobile telephone or tabletexecuting the Android operating system (Android is a trade mark ofGoogle Inc.).

In the example shown in FIG. 1, the ultrasound scanner 2 comprises abody 5 and a separate ultrasound probe 3 which is connected to the bodyby a detachable cable. However, in some embodiments, the ultrasoundscanner is a single integral unit (having a single casing) functioningas an ultrasound probe.

The ultrasound data processor has a display screen 50. The ultrasounddata processor may be a single unit, however its functionality may bedistributed between a plurality of units or devices. In some embodimentsvideo generated by the ultrasound data processor is additionally oralternatively displayed on a remote display, for example on goggles wornby a user. The apparatus is used to generate ultrasound images of a scanregion of an animal and to display these images to the user in real timeso that the user can rapidly and accurately carry out a scanning task.

The ultrasound scanner 2 comprises a microprocessor executing a storedprogram, functioning as a controller 20. The controller regulates thescanning procedure, subsequent data processing and transmission. Theultrasound scanner has a one-dimensional (curved or straight line) arrayof ultrasound transducers 24, within the ultrasound probe (functioningas the ultrasound probe region), and a transmit beamformer 22(comprising the transmit circuitry) which generates electrical signalsin use to drive the ultrasound transducers to generate ultrasound pulsesfocussed in turn on specific scan positions 6 as they travel along scanlines 8 within a scan region 10.

The scanner further comprises a receive beamformer 26 (the beamprocessor, comprising the receive circuitry) configured to extractultrasound pulse echoes from measurements made by the ultrasoundtransducers and a beamformed data processor 28 configured to carry outstandard data processing steps on raw ultrasound data such as band-passfiltering, detection and log compression.

A compressor module 30 is configured to receive and compress ultrasoundframe data output by the beamformed data processor and there is a Wi-Fitransceiver 32 (functioning as the wireless transmitter), having atransmit buffer 34, for transmitting compressed data from the compressormodule in use. The scanner includes an internal (replaceable orintegral) battery (optional rechargeable) which supplies all of thepower to the scanner during use. The scanner may also have an interfacefor receiving power from an external source (e.g. a power cable) butexternal power sources may often be unavailable.

The ultrasound data processor 4 comprises a Wi-Fi transceiver 40(functioning as the wireless receiver) and a decompression module 42configured to decompress compressed ultrasound frame data received fromthe Wi-Fi transceiver. Wi-Fi is a wireless radio transmission protocolspecified by the IEEE 802.11 standards. (Wi-Fi is a trade mark of theWi-Fi Alliance).

An image processor 44 is provided to calculate ultrasound image datafrom the ultrasound frame data and is in electronic communication with adisplay interface 46 which transmits images to the display screen 50 inuse for display.

One skilled in the art will appreciate that the extent to which thefunctionality of the components of the ultrasound scanner and ultrasounddata processor are implemented as standalone circuits or as program codeinstructions executed by the microprocessor is a matter of designchoice. For example, the compressor and decompressor might beimplemented by the microprocessor executing program code or withdedicated circuits. The transmit beamformer, receive beamformer andWi-Fi transceivers include dedicated circuitry but may be implemented inpart by the microprocessor.

In embodiments in which the ultrasound scanner comprises both a body 5and an ultrasound probe 3 the distribution of the components shown inFIG. 1 between the body and probe is a matter of design choice. Some orall of the transmit and receive circuitry, for example, may be in theultrasound probe along with the transducers.

With reference to FIG. 2, during operation the controller 20 regulatesthe transmit beamformer to generate 100 ultrasound pulses which arefocussed in turn on scan positions 6 spaced apart along the length ofscan lines 8 in the scan region 10. Ultrasound echoes are received 102by the ultrasound transceiver array and beamformed 104. The controllerregulates the rate at which ultrasound frames are scanned, the number ofscan lines in each ultrasound frame and the number of scan positions ineach scan line. One skilled in the art will be aware of standardultrasound techniques for controlling transmit and receive beamformersto scan the scan positions.

Thus, the ultrasound scanner transmits ultrasound pulses from a numberof transducers, progressively along individual scan lines, and repeatsthe process to scan line across the scan region which is effectively aslice through a region of interest. The process is then repeated torescan the region of interest. The data concerning each scan through theregion of interest is an ultrasound frame.

The beamformed data is processed 106 by the beamformed data processor28. This signal processing step includes data processing steps which aretypically carried out on raw beamformed ultrasound measurement data suchas band-pass filtering, detection and log compression. The beamformeddata processor processes data concerning individual frames one at a timeand within each frame processes data concerning individual scan linesone at a time.

The output from the beamformed data processor is ultrasound frame data60, which comprises a plurality of scan line data structures 62. Eachscan line data structure relates to echoes received at different depthswithin individual scan lines. In this example, the scan line data is ameasurement of echo brightness with depth (z) in a specific scan line.The scan line data structure also includes meta-data indicating to whichslice the measurement data relates, for example it may specify an x andy position (relative to the transceiver array), angle, line length andnumber of scan points and/or distance between scan points. The scanlines are typically grouped in data structures concerning individualultrasound frames, although this is not essential.

The data compression module compresses 110 the ultrasound frame data. Inthis example, the scan line data structures are processed in turn. Thedifference between consecutive measurements within the scan line datastructure is calculated and then a variable length coding algorithm(such as Huffman coding, Lempel-Ziv coding or arithmetic coding) is usedto encode those differences. We have found that, due to typical spatialvariation of ultrasound echo intensities, this compression approach isefficient. In this example, the data concerning individual scan linesare compressed individually, i.e. the compressed data comprising datastructures representing individual scan lines without reference to otherscan lines. Furthermore, the compressed data relating to individualultrasound frames represents individual ultrasound frames withoutreference to previous ultrasound frames. Meta-data need not becompressed. Using a 6-bit Huffman type variable length coding algorithmwe have obtained data compression of about 50%.

Data generated by the data compression module is passed to the Wi-Fimodule for wireless transmission 110 to the image processor. Thecompressed data is stored in the transmit buffer of the Wi-Fi moduleuntil it is transmitted. The compressed data is received 112 by theWi-Fi module of the image processor.

The decompression module 42 then decompresses the received ultrasoundframe data, by reversing the variable length encoding process torecreate the ultrasound frame data. Typically, the compression anddecompression process is lossless and the ultrasound frame data can befaithfully reproduced, however it is not essential that this procedureis lossless.

The image processing module 44 then processes the decompressedultrasound frame data and carries out typical ultrasound imagegeneration procedures 116 known to the person skilled in the art, suchas scan conversion, angle compounding frame smoothing, boundary/edgedetection and so forth, and generate pictures, being individual imageframes for consecutive display on a display 46 of the image processor.The image processor may be the microprocessor which functions as thecontroller (the CPU of the device) however video processing may becarried out with a dedicated graphics processing unit, for example usingOpenGL with individual scan lines represented as OpenGL polygons.

The resulting images are then displayed on the display screen 50 oroutput through a video output interface (typically to a remote displayscreen, e.g. wirelessly). The images are displayed in real time, within0.25 s of the ultrasound measurements which gave rise to the images. Theuser can therefore manoeuvre the ultrasound probe region (which may beinvolve manoeuvring the ultrasound scanner as a whole if it is integral,or simply manoeuvring an ultrasound probe) to view a region of interestof an animal.

We have found that this variable data rate can enable higher resolutionimages to be prepared when a given wireless data transmission bandwidthpermits but in particular it enables video images to be maintained withreasonable latency even if the bandwidth of the Wi-Fi connection issub-optimal. This makes the invention especially useful in a veterinarycontext where ultrasound images may need to be obtained in uncontrolledenvironments, such as outdoors or in farm buildings.

Still further, the controller includes a buffer monitor 36, which istypically program code executed periodically by the microprocessor orevent triggered, which monitors the Wi-Fi buffer determines when theamount of data stored in the Wi-Fi transmit buffer 34 exceeds athreshold. This indicates that the bandwidth of the Wi-Fi transmissionhas decreased.

When that occurs, the controller changes the rate of scanning to reducethe rate at which scan data is generated by one or more of:

-   -   Reducing the number of scan positions in each scan line (e.g.        omitting every alternate scan position)    -   Reducing the number of scan lines (e.g. omitting alternate scan        lines)    -   Reducing the number of scan lines which are scanned during each        frame (e.g. scanning a scan line at a particular orientation        during only some frames)    -   Reducing the frame rate.

Thus, the rate at which scan data is generated is reduced. Typically thecontroller has a predefined priority order in which it proceeds throughthe different data reduction operations set out above if the transmitbuffer size continues to increase. This has the side-effect of reducingpower consumption by the ultrasound transmit circuitry.

In some embodiments, the rate of scanning is maintained but instead themeasured ultrasound frame data is processed to omit (e.g. delete, notcopy or not process) data concerning some (e.g. alternate) scanpositions, or some (e.g. alternate) scan lines, or even to omit entireultrasound frames without reducing the rate of scanning. This would nothowever reduce the power consumption of the ultrasound transmitcircuitry.

The image processor can adapt to a reduction in the number of scanpoints in each line or number of scan lines by reducing the resolutionof an image. If some or all scan points or scan lines are only includedin some (e.g. alternate) ultrasound frames, the image processor canadapt to this by retaining values of the strength (e.g. intensity,amplitude or brightness) of ultrasound echoes from a scan location untilfurther data concerning that scan location is received. If dataconcerning specific scan points, or scan lines is no longer available,the calculated resolution of the images concerning those scan points canbe reduced or the strength of ultrasound echoes from the respective scanpoints or scan lines can be estimated by interpolation.

Furthermore, the rate of scanning can be reduced within an ultrasoundframe. This allows a rapid response to changes in wireless transmissionbandwidth or rapid recovery from intermittent data loss. If data is notreceived for a scan point or scan line, the previous values ofultrasound echo strength used by the image processor for that locationmay persist for a period of time, or may be estimated by interpolation.

In an example, in a default mode when there is sufficient Wi-Fibandwidth, each frame comprises 128 scan lines with 480 scan positionsper line, the measurement for each sample is represented as an 8 bitnumber; and there are 30 frames per second. Accordingly about 14 Mb/s ofultrasound frame data is generated. This is compressed to below 10 Mb/sand transmitted to the ultrasound data processor with a latency of below0.1 seconds. If the transmit buffer begins to fill up, the number ofscan positions per line might be reduced (e.g. to 240 then 120), thenumber of scan lines can be reduced (e.g. to 64) and the scan rate canbe reduced (e.g. to 15 frames per second), reducing the transmit raterequirement to less than 1 MB/s. On the other hand, if images weregenerated by the ultrasound scanner and transmitted as MPEG compressedvideo, a minimum of 6 Mb/s would be required, there would be a latencyof around 0.3 seconds as groups of 10 pictures would be encoded togetherand the video images would stop entirely, skip images or suffersubstantial latency if there were intermittent reductions in Wi-Fitransmission rate.

However, using the methods of the present invention we have obtained alag of as low as 70-90 milliseconds. For example, in an example with atime between ultrasound frames of 40 mS, plus transmit time of 3 mStransmitting a 5 GHz/18 mS transmitting at 2.4 GHz plus processing time(e.g. 20 mS) and time to render (10 mS) we have achieved a lag of 73 mS(transmitting at 5 GHz) or 88 mS (transmitting at 2.4 GHz) and imageshave continued to be updated continuously, possibly with a reduction inimage quality, despite environmental variations affecting transmissionrate which would have lead to gaps in the image stream transmitted byMPEG through the same bandwidth.

The invention claimed is:
 1. Ultrasound imaging apparatus comprising anultrasound scanner and a separate ultrasound data processor: theultrasound scanner comprising: one or more ultrasound sources andreceivers, transmit circuitry configured to apply electrical signals tothe ultrasound sources to transmit ultrasound pulses into a scan region,receive circuitry configured to measure ultrasound echoes received atthe ultrasound receivers from the scan region, a beam processorconfigured to process the measured ultrasound echoes and outputultrasound frame data, the ultrasound frame data comprising measurementsof ultrasound echoes from each of a series of scan positions in the scanregion, a data compressor configured to process ultrasound frame dataoutput by the beam processor to generate compressed ultrasound framedata, and a wireless transmitter configured to wirelessly transmit thecompressed ultrasound frame data; the ultrasound data processorcomprising: a wireless receiver configured to receive the compressedultrasound frame data transmitted by the wireless transmitter, a datadecompressor configured to decompress compressed ultrasound frame datareceived by the wireless transmitter, an image processor configured toprocess decompressed data output by the data decompressor to formultrasound images of the scan region, and a display interface whereinthe ultrasound frame data comprises ultrasound line data portions whichspecify the measured strength of ultrasound echoes received by one ormore ultrasound receivers from a series of spaced apart positions alonga line and the data compressor is configured to output compressedultrasound frame data in which each individual ultrasound line iscompressed separately.
 2. Ultrasound imaging apparatus according toclaim 1, wherein the data compressor is configured to output compressedultrasound frame data in which each individual ultrasound frame iscompressed independently of any other frame.
 3. Ultrasound imagingapparatus according to claim 1, wherein the data compressor isconfigured to calculate and encode the differences between consecutivemeasurements within ultrasound line data portions.
 4. Ultrasound imagingapparatus according to claim 1, wherein the data compressor is avariable length code compressor.
 5. Ultrasound imaging apparatusaccording to claim 1, wherein the ultrasound scanner is configured toregulate the number of scan positions per unit of measurement time ofthe ultrasound frame data which is transmitted by the wirelesstransmitter, in compressed form, responsive to a received variablerelating to a transmission property of the wireless transmitter. 6.Ultrasound imaging apparatus according to claim 5, wherein regulatingthe number of scan positions per unit of measurement time of theultrasound frame data which is transmitted by the wireless transmittercomprises one or more of: regulating the number of scan positions perscan line in respect of which compressed ultrasound frame data istransmitted; regulating the number of scan lines per ultrasound frame inrespect of which compressed ultrasound frame data is transmitted; andregulating the period between ultrasound frames in respect of whichcompressed ultrasound frame data is transmitted.
 7. Ultrasound imagingapparatus according to claim 6, wherein the number of scan positions perunit of time in respect of which compressed ultrasound frame data istransmitted is reduced progressively through a plurality of differentmodes, which differ in terms of the number of scan positions in respectof which compressed ultrasound frame data is transmitted, in apredetermined order, the modes differing in terms of one or more of: thenumber of scan positions per scan line, the number of scan lines perultrasound frame and/or the period between ultrasound frames and whereinthe apparatus is configured to vary the number of scan positions perunit of measurement time in respect of which data is transmitted withinan ultrasound frame.
 8. Ultrasound imaging apparatus according to claim1, configured to regulate the number of scan positions per unit of time,responsive to a received variable relating to a transmission property ofthe wireless transmitter.
 9. Ultrasound imaging apparatus according toclaim 8, configured to regulate the number of scan positions per unit oftime which are scanned by: regulating the number of scan positions perscan line; regulating the number of scan lines per ultrasound frame;regulating the period between ultrasound frames.
 10. Ultrasound imagingapparatus according to claim 9, configured to regulate the number ofscan positions per unit of time which are scanned progressively througha plurality of different modes, which differ in terms of the number ofscan positions which are scanned, in a predetermined order, the modesdiffering in terms of one or more of: the number of scan positions perscan line, the number of scan lines per ultrasound frame and/or theperiod between ultrasound frames.
 11. Ultrasound imaging apparatusaccording to claim 5, wherein the received variable relating to atransmission property of the wireless transmitter is a measurementrelated to the amount of data in a transmit buffer of the wirelesstransmitter.
 12. Ultrasound imaging apparatus according to claim 1,wherein the time lag between ultrasound echoes being received by theultrasound receivers and the display of the ultrasound image calculatedby processing measurements of those ultrasound echoes is less than 0.2seconds and/or is less than 5 times the period between ultrasoundframes.
 13. A method of processing ultrasound echo data to form images,the method comprising: at an ultrasound scanner comprising one or moreultrasound sources and receivers, receiving ultrasound echoes from ascan region, processing measurements of the received ultrasound echoesto thereby calculate ultrasound frame data, the ultrasound frame datacomprising measurements of ultrasound echoes from each of a series ofscan positions in the scan region, compressing the ultrasound frame datato generate compressed ultrasound frame data, transmitting thecompressed ultrasound frame data through a wireless transmitter to awireless receiver of an ultrasound data processor, at the ultrasounddata processor, decompressing the received ultrasound frame data,processing the decompressed data to form ultrasound images of theportion of the subject, and outputting the ultrasound images, whereinthe method comprises compressing each ultrasound line separately.
 14. Amethod according to claim 13, wherein the compressed ultrasound framedata which is generated comprises data portions each of which representsan individual ultrasound frame compressed independently of any otherframe.
 15. A method according to claim 13, wherein the ultrasound framedata comprises ultrasound line data portions which specify the measuredstrength of ultrasound echoes received by one or more ultrasoundreceivers from a series of spaced apart positions along a line and thecompressed ultrasound frame data comprises data portions each of whichrepresents an individual ultrasound line without reference to any otherultrasound line data.
 16. A method according to claim 13, whereincompressing the ultrasound frame data comprises applying a variablelength code compression algorithm to the ultrasound frame data.
 17. Amethod according to claim 13, comprising controlling transmit circuitryto apply electrical signals to the ultrasound sources to transmitultrasound pulses into the scan region, and receiving a variablerelating to a transmission property of the wireless transmitter andvarying the number of scan positions per unit of measurement time of theultrasound frame data which is transmitted by the wireless transmitter,in compressed form, responsive thereto, wherein regulating the number ofscan positions per unit of measurement time of the ultrasound frame datawhich is transmitted by the wireless transmitter comprises one or moreof: regulating the number of scan positions per scan line in respect ofwhich compressed ultrasound frame data is transmitted; regulating thenumber of scan lines per ultrasound frame in respect of which compressedultrasound frame data is transmitted; and regulating the period betweenultrasound frames in respect of which compressed ultrasound frame datais transmitted.
 18. A method according to claim 17, wherein the numberof scan positions per unit of time in respect of which compressedultrasound frame data is transmitted is reduced progressively through aplurality of different modes, which differ in terms of the number ofscan positions in respect of which compressed ultrasound frame data istransmitted, in a predetermined order, the modes differing in terms ofone or more of: the number of scan positions per scan line, the numberof scan lines per ultrasound frame and/or the period between ultrasoundframes and/or wherein the number of scan positions per unit ofmeasurement time in respect of which data is transmitted is variedwithin an ultrasound frame.
 19. A method according to claim 13,comprising regulating the number of scan positions which are scanned perunit of time, responsive to a received variable relating to atransmission property of the wireless transmitter, wherein the number ofscan positions per unit of time which are scanned is regulated by:regulating the number of scan positions per scan line; regulating thenumber of scan lines per ultrasound frame; regulating the period betweenultrasound frames.
 20. A method according to claim 19, comprisingvarying the number of scan positions per unit of time which are scannedprogressively through a plurality of different modes, which differ interms of the number of scan positions which are scanned, in apredetermined order, the modes differing in terms of one or more of: thenumber of scan positions per scan line, the number of scan lines perultrasound frame and/or the period between ultrasound frames.